Stereo recordings and other multichannel audio signals may comprise one or more components designed to give a listener the sense that a particular source of sound is positioned at a particular location relative to the listener. For example, in the case of a stereo recording made in a studio, the recording engineer might mix the left and right signal so as to give the listener a sense that a particular source recorded in isolation of other sources is located at some angle off the axis between the left and right speakers. The term “panning” is often used to describe such techniques, and a source panned to a particular location relative to a listener located at a certain spot equidistant from both the left and right speakers (and/or other or different speakers in the case of audio signals other than stereo signals) will be referred to herein as a “panned source”.
A special case of a panned source is a source panned to the center. Vocal components of music recordings, for example, typically are center-panned, to give a listener a sense that the singer or speaker is located in the center of a virtual stage defined by the left and right speakers. Other sources might be panned to other locations to the left or right of center.
The level of a panned source relative to the overall signal is determined in the case of a studio recording by a sound engineer and in the case of a live recording by such factors as the location of each source in relation to the microphones used to make the recording, the equipment used, the characteristics of the venue, etc. An individual listener, however, may prefer that a particular panned source have a level relative to the rest of the audio signal that is different (higher or lower) than the level it has in the original audio signal. Therefore, there is a need for a way to allow a user to control the level of a panned source in an audio signal.
As noted above, vocal components typically are panned to the center. However, other sources, e.g., percussion instruments, also typically may be panned to the center. A listener may wish to modify (e.g., enhance or suppress) a center-panned vocal component without modifying other center-panned sources at the same time. Therefore, there is a need for a way to isolate a center-panned vocal component from other sources, such as percussion instruments, that may be panned to the center.
Finally, listeners with surround sound systems of various configurations (e.g., five speaker, seven speaker, etc.) may desire a way to “upmix” a received audio signal, if necessary, to make use of the full capabilities of their playback system. For example, a user may wish to generate an audio signal for a playback channel by extracting a panned source from one or more channels of an input audio signal and providing the extracted component to the playback channel. A user might want to extract a center-panned vocal component, for example, and provide the vocal component as a generated signal for the center playback channel. Some users may wish to generate such a signal regardless of whether the received audio signal has a corresponding channel. In such embodiments, listeners further need a way to control the level of the panned source signal generated for such channels in accordance with their individual preferences.